Fabrication of ferromagnetic-semiconductor heteroepitaxial structures using ferromagnetic Ba ferrite films

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In order to realize ferromagnetic-semiconductor structures with high quality, growth conditions of magnetic oxide layrs on semiconductors were investigated. The results are as follows :1.It was found for the first time that ferromagnetic Fe_3O_4 (100) thin films are epitaxially grown on GaAs (100) substrates at 200ﾟC by electron beam evaporation, when the subtrates were sulphur-terminated using an (NH_3) _4S_x solution. The thin films deposited at substrate temperatures above 200ﾟC were polycrystalline. This is associated with desorption of sulphur and resultant oxidization of the GaAs surface. The Fe_3O_4 (100) epitaxial thin films with higher quaslity were grown at 450ﾟC on the above thin films, with the in-plane alignment of Fe_3O_4 [100]//GaAs [100]. Atomic force microscopy and X-ray photoelectron spectroscopy showed that the crystalline quality and morphology of the epitaxial thin films primarily depend on the lattice mismatch between the film and the substrate. No epitaxial growth of Fe_3O_4 thin films and alpha-Fe_2O_3 thin films coccurred on hydrogen-terminated Si (100) and (111) havinb a lattice constant similar to that of GaAs. These results indicate the effectiveness of surface-termination using ions stable to oxygen, for preventing the semiconductor surface from oxidizing in the early stage of the deposition.2. It was found that the (0001) single crystalline thin films of ferromagnetic Ba hexaferrite are epitaxially grown on the buffer layrs of alpha-Fe_2O_3 and alpha-Al_2O_3 (0001) by sputtering.The above results indicate that the heteroepitaxial structure system of a semiconductor and a ferromagnetic oxide with strong magnetic anisotropy which is a goal of this research may be achieved using Co-substituted Fe_3O_4 instead of Ba hexaferrite as a ferromagnetic layr and GaAs as a semiconductor.